Cavity Polaritons Formed from Spatially Separated Quasi-degenerate Porphyrin Excitons: Structural Modulations of Bright and Dark State Energies and Compositions

Abstract

In this study, we assess the properties of cavity polaritons formed from the strong coupling of photons to nearly degenerate molecular excitons located in separate layers of multilayer Fabry−Perot resonators. By embedding copper(II) tetraphenylporphyrin (CuTPP) and free base tetraphenylporphyrin (H 2 TPP) in separate layers of the intracavity region, we present evidence of cavity polariton formation using angularly resolved transmission spectra. Multichromophore models enable our characterization of the polariton states consistent with our experimental results. The results show the existence of a middle polariton state whose photonic content does exceed 5% for any fabricated sample, which makes these states spectroscopically dark. We use models of the excited state potential energy surfaces of each porphyrin molecular species to compute and characterize modulations of multipolariton energies due to atomic motions along the reorganizational coordinate of each chromophore. These calculations indicate modulations of each molecule's structure lead to changes in the composition and energy of the multipolariton states. In particular, by modulating the structure of H 2 TPP, which possesses a lower energy Soret transition, we can drive excitonic resonances that cause the photonic content of the MP state to oscillate between zero and nonzero values. Our results and analysis suggest multipolariton formation from quasi-degenerate molecular excitons could provide means to optoelectronic devices such as THz-rate light modulators useful for classical and quantum information processing protocols.

Rational Design of Molecular Cavity Polariton Relaxation

“…The left and right panels of Figure 5 show this relatively increased suppression of the excitonic disorder even though the absorption spectrum of Zn2U molecules possesses nearly twice the inhomogeneous broadening of that of H2TPP, as we showed previously. 40 We argue that these two factors account for the qualitatively different values of α necessary for our effective modeling of ΓLP in each sample, as seen in Figure 5 and reported in Table 1.…”

“…For the first sets of samples, we designed and fabricated multilayer, Fabry-Pérot (FP) micro-resonators whose 3λ/2-mode maintains photons that interact resonantly with the Soret transitions of free base tetraphenyl porphyrin (H2TPP) and copper (II) tetraphenyl porphyrin (CuTPP) localized in distinct layers of the intracavity region, which we described previously. 40 While the Soret transitions of these chromophores possess nearly degenerate energies, our analysis of the cavity multipolaritons formed through collective strong light-matter coupling indicates that excitons localized on the H2TPP molecules comprise the LP state more significantly than their counterparts on CuTPP. While the top panel of Figure 1 shows a three-level Hamiltonian described previously 40 the dispersion of peaks in the angularly-resolved transmission spectra of the loaded multilayer FP cavity, the bottom panel of Figure 1 shows the CuTPP excitons never comprise more than 20% of the LP state.…”

“…40 While the Soret transitions of these chromophores possess nearly degenerate energies, our analysis of the cavity multipolaritons formed through collective strong light-matter coupling indicates that excitons localized on the H2TPP molecules comprise the LP state more significantly than their counterparts on CuTPP. While the top panel of Figure 1 shows a three-level Hamiltonian described previously 40 the dispersion of peaks in the angularly-resolved transmission spectra of the loaded multilayer FP cavity, the bottom panel of Figure 1 shows the CuTPP excitons never comprise more than 20% of the LP state. In contrast, the H2TPP excitons contribute increasingly larger amounts to the LP state as we increase θinc.…”

Molecular Vibrational Polariton Dynamics: What Can Polaritons Do?

“…To realize it, we tuned the cavity so that its resonance is between the asymmetric vibrational modes of W­(CO) 6 and W­( 13 CO) 6 , leading to a three-polariton system. ,− We ensured that the coupling strength was high enough that the UP, MP, and LP were composed of the two vibrational modes and the single cavity mode, as indicated by their Hopfield coefficients. Noticeably, the UP was primarily composed of W­(CO) 6 and the cavity mode, with a small contribution from W­( 13 CO) 6 (Figure D).…”

Cavity Control of Molecular Spectroscopy and Photophysics

“…Molecular polaritons, either vibrational or electronic, can have an significant influence on the optical, electronic, and chemical properties of molecules . The dynamical phenomena observed in optical cavities, mostly with the Fabry–Perot geometries, include demonstration of molecular exciton cavity polaritons, polariton lasing using a molecular material, polariton-mediated energy transfer between conventional − and vibrational donors and acceptors, cavity polaritons formed from molecules located in different regions of a multilayer Fabry–Perot resonator, and collective strong light–matter coupling effects in the ultrafast nonradiative relaxation processes in polariton states . Examples involving chemical reactions include modified photoisomerization rates and reversing the branching ratio in ground-state chemical reactions. − An intensive theoretical effort has been made toward understanding the mechanism behind polariton-mediated processes and their experimental signatures. , Very recent theoretical studies include two-photon absorption of entangled photon pairs by cavity polaritons and X-ray spectroscopy in a cavity where different core electrons couple via polariton formation …”